Stroke was, prior to 1980, the leading cause of death in this country, but has decreased by a factor of approximately 4 during the last 20 years, due to the progress in medical technology and development of emergency medical care. However, nowadays a rapid advance of an aging society tends to increase the number of stroke patients again. For the prevention thereof, daily health care is important. In addition, a patient's life can be prolonged by accurately determining the cause of disturbance of consciousness at an early stage of stupor or coma caused by stroke or the like, and selecting one or more appropriate options (a treatment, prognosis assessment, or the like).
Strokes are brain disorders caused by abnormalities in blood vessels (a paroxysmal disorder in which a cerebral blood vessel is ruptured or clogged due to a certain cause). An early and appropriate treatment is important, because stroke endangers the life or leaves sequelae such as paralysis or logopathy.
Strokes can be classified into two major categories: hemorrhage due to the rupture of a cerebral blood vessel, and ischemia due to the blockage of a cerebral blood vessel. Hemorrhagic strokes include subarachnoid hemorrhage and intracerebral hemorrhage, and ischemic strokes include cerebral infarction and transient ischemic attack.
Cerebral infarction, caused by the blockage of a cerebral artery by a thrombus, is the main type of strokes which are the third leading cause of death in Japan, and has a high mortality rate. Cerebral infarction is a state in which a cerebral artery is clogged due to a certain cause and, as a result, the blood flow to the subsequent tissues is disrupted or reduced. Approximately 20% of the total causes of death are cerebrovascular diseases, and cerebral infarction accounts for approximately 50% of these diseases. Cerebral infarctions can be classified into two major categories: cerebral embolism and cerebral thrombosis. Cerebral embolism is not directly caused by abnormalities in cerebral arteries, but is caused by an aggregate (such as blood, proteins, lipid, or the like) which is formed in the heart, due to a heart disease, accelerated to cerebral arteries, and blocks a cerebral artery. By contrast, cerebral thrombosis is developed due to arteriosclerosis of cerebral arteries itself. Cerebral thrombosis is more frequent than cerebral embolism.
As well as stroke, the causes of stupor or coma include, for example, the damage of the brain stem due to head injury or the like, alcoholism, an overdose of a drug such as a sedative, cardiac arrest, aneurysm, a severe pulmonary disease, inhalation of carbon monoxide, ictus epilepticus, hypothyroidism, hepatic failure, renal failure, hypoglycemia caused by diabetes, and the like. Therefore, many examinations are necessary to make a precise decision. For example, blood levels of sugar, sodium, alcohol, oxygen, carbon dioxide, and the like, counts of red blood cells and white blood cells, or sugar and toxic substances in urine, can be examined. Further, troponin or a heart-specific fatty acid-binding protein (H-FABP) may be measured to determine whether stupor or coma in a patient is caused by myocardial infarction, and an appropriate treatment may be selected. However, examples of a diagnostic method for arteriosclerosis as a cause of cerebral thrombosis include noninvasive examinations, such as fundoscopy, X-ray CT, MRI, a pulse wave velocity method, or blood flow monitoring using an ultrasonic wave, and invasive examinations, such as angiography, angioscopy, or intravascular ultrasound analysis. These methods are insufficient to monitor the extent of arteriosclerotic vascular disease or the progress of its symptoms.
It was suggested that a von Willebrand factor (hereinafter referred to as vWF)-cleaving protease [hereinafter referred to as ADAMTS13 (another name of the vWF-cleaving protease)] is involved in the onset of thrombotic thrombocytopenic purpura (TTP) which is very severe and has a high mortality rate; the vWF-cleaving protease was purified from plasma (nonpatent reference 1); and the gene was identified by cDNA cloning. It was actually revealed that genetic mutations of ADAMTS13 remarkably reduced the vWF-cleaving activity (nonpatent reference 2). An enzyme immunoassay utilizing monoclonal or polyclonal antibodies specific to ADAMTS13 was recently developed (patent reference 1), and a method for detecting causes of thrombosis involved in platelet aggregation, and the degree of thrombophilia in thrombosis was established. This method was used to find that the concentrations of ADAMTS13 contained in plasma samples collected from patients with thrombosis were remarkably lowered in comparison with those from healthy people.
For example, patent reference 2 discloses a method of detecting thrombosis or the degree of thrombophilia, characterized by measuring ADAMTS13, and discloses that examples of thrombosis include acute or chronic myeloid leukemia, acute promyelocytic leukemia, systemic lupus erythematosus, pulmonary embolism, cerebral infarction, veno-occlusive disease, acute lymphocytic leukemia, thrombotic microangiopathy, thrombotic thrombocytopenic purpura, hemolytic uremic syndrome, and deep vein thrombosis. Further, patent reference 3 discloses a method of detecting platelet thrombosis or organ failure in a patient suffering from disseminated intravascular coagulation (DIC) or systemic inflammatory response syndrome (SIRS), by analyzing ADAMTS13 and/or a cleaving factor thereof (such as elastase, plasmin, or thrombin).
As a conventional method for determining the ADAMTS13 activity, a method of the detection of large vWF multimers, using a combination of an SDS-agarose electrophoresis and autoradiography or Western blotting, was used (nonpatent reference 3). Further, FRETS-VWF73, which is prepared by introducing a fluorescent group and a quenching group into 73 residues of the A2 domain (i.e., the specific cleavage sites by ADAMTS13) of vWF, was developed and enabled the measurement of the ADAMTS13 activity to be conveniently performed (nonpatent reference 4).    [patent reference 1] WO 2004/029242    [patent reference 2] WO 2005/062054    [patent reference 3] WO 2006/049300    [non-patent reference 1] K. Fujikawa et al., Blood, (U.S.A.), 2001, vol. 98, p. 1662-6    [non-patent reference 2] G. G. Levy et al., Nature, (United Kingdom), 2001, vol. 413, p. 488-494    [non-patent reference 3] M. Furlan et al., Blood, (U.S.A.), 1996, vol. 87, p. 4223-4234    [non-patent reference 4] Kokame K et al., The British Journal of Haematology, (United Kingdom), 2005, vol. 129, p. 93-100